Were you running PowerShell as an administrator when you ran Update-Help? As a test, try accessing one of the files directly, like Get-Help about_Operators , and see if that works.
On a side note, a did a quick web search on “German PowerShell help”, and you may be running into some problems there if some or all of the help content hasn’t been translated yet. One suggested workaround was to attempt to load the English language help files like this:
Only by changing your regional / language settings. The command appears to default to using [System.Threading.Thread]::CurrentThread.CurrentUICulture and [System.Threading.Thread]::CurrentThread.CurrentUICulture.Parent, if you haven’t specified anything with the -UICulture parameter.